Production of rustless iron



Patented Apr. 12, 1938 PRODUCTION or RUSTLIESS IRON Alexander I}. Feild,Baltimore, Md, assignor to Rustless Iron and Steel Corporation,Baltimore, Md., a corporation of Delaware No Drawing. Originalapplication May 31, 1934,

Serial No. 728,415. Divided and this application September 11, 1936,Serial No. 100,381

3 Claims.

This application is a division of my United States Letters Patent2,076,885 of April 13,1937 entitled Production of rustless iron, and theinvention relates to the manufacture of chromiummanganese irons andsteels, and especially to the manufacture of chromium-manganese irons ofhigh chromium and manganese contents and low carbon contents.

Among the objects of my invention is the eflicient, economical andthoroughly practical production of chromium-manganese irons and steels.(irons and steels analyzing approximately, chromium 10% to 35%,manganese 6% to 20%, carbon .05% to .15% for the alloy iron and .15% to1% for the alloy steel, together with desired supplementary additions ofnicke copper, aluminum, silicon, molybdenum, tun ,.,ten and the like forspecial purposes and with the usual low percentages of sulphur andphosphorus and the balance substantially iron), and especially to thesimple, direct and thoroughly reliable production of chromium-manganeseirons, employing inexpensive and readily available raw materials andutilizing known furnacing and operating equipment.

The invention accordingly consists in the combination of elements,mixture of materials and composition of ingredients and in the severalsteps and the relation of each of the same, to one or more of the othersas described herein and the scope of the application of which isindicated in the following claims.

As conducive to a clearer understanding of certain features of myinvention it may be noted at this point that in various marine,aviation,

automotive, industrial and architectural applications where a brightsurface pleasing to the eye and resistant to the corrosive attack ofvarious acid, alkali or salt atmospheres or solutions is required, orwhere metal which is strong, tough and durable and resistant to thecorrosive attack of' various acids, alkalies and salts at high tem-.

peratures is required, the well known austenitic chromium-nickel ironsand steels are in widespread use at the present time. The extent of theuse of such alloy irons and steels is greatly handicapped, however, bythe comparative great expense of these materials as compared withordinary irons and steels which are less attractive to do the eye andwhich are less resistant to corrosive attacks of the atmosphere orvarious acid, alkali and salt-mediums.

While numerous substitutes have been proposed for the expensiveaustenitic chromium-nickel irons and steels the only alloy iron or steelwhich used methods of production the expensive sources of chromium andmanganese, are added to a bath of low carbon iron maintained at adesired temperature. Such methods of production, while simple inprocedure, require prolonged heating with a continuous consumption ofpower and yield a very expensive product, largely because of the greatexpense of the raw materials used in obtaining the alloying additions,chromium and manganese.

While known methods of producing chromium-' manganese irons and steelsare ordinarily satisfactory in the production of the usual low chromiumlow manganese alloys these methods as applied to the production of highchromium high manganese austenitic irons and steels render the productprohibitively expensive. In fact, the cost of producing the austeniticchromium-manganese irons and steels in accordance with known and/or usedmethods is so great that the margin of savings over the production ofthe well-known austenitic chromium-nickel irons and steels is so smallthat there is little incentive to replace, for general purposes, thesecostly irons and steels with the chromium-manganese irons and steels.

One of the outstanding objects of my invention, therefore, is theproduction of high chromium high manganese irons and steels, andespecially the production of austenitic chromium-manganese irons in asimple, direct and economical manner employing inexpensive and readilyavail able raw materials in the most economical proportions dependingupon the availability and fluctuations in current market prices,achieving high grade, sound/clean metal which may be manufactured andsold at a price considerably beneath that of the comparatively expensivechromium-nickel irons and steels and which may be introduced into awider range of applications supplanting known inferior but lessexpensive metals.

In the practice of my invention a material high in manganese content,such as any one of the manganese ores, pyrolusite MI1O2, manganiteMnOlOH), hausmannite 'MnsO i, braunite 3Mn2O3.MnSiO3, rhodocrosite MnCOxand/or high carbon ferromanganese (produced by smelting any one of theabove ores with coke achieving a product analyzing approximately, iron10% to 30%, manganese 80% to 60%, silicon 1% and carbon 5% to 8%) ismelted down in a suitable furnace with chrome ore FeOCmOa and/or highcarbon ferrochrome (produced by smelting this ore with coke and silicaachieving a product analyzing approximately, 60% to 70% chromium, 4% to7% carbon, 20% to 30% iron) and a desired quantity of available lowcarbon steel scrap, either with or without a readily available amount ofhigh chromium high manganese iron or steel scrap or straight chromiumrustless iron or steel scrap or high manganese iron or steel scrap, anda sufficient quantity of an oxidizing agent, such as roll scale ormagnetic iron ore concentrate to exclude and/or remove carbon from theingredients, thereby forming a bath of ferrous metal containingmanganese and chromium with an overlying oxidizing slag rich in theoxides of chromium and manganese.

To assure the production of sound metal, free from gas-pockets, pits andthe like, the large quantities of ore used are, preferably, thoroughlydried at a high temperature prior to charging into the furnace. Thepre-drying of the ores is carried out in any suitable manner, as by along heating in a rotary gas-fired kiln at such temperatures as to ridthe ores of substantially all free and combined moisture normallypresent. The use of predried materials effectively minimizes the amountof moisture introduced into the furnace and consequently limits theamount of hydrogen available to contaminate the metal during melt-down,as a result of the decomposition of this moisture by the action of theelectric furnace arcs, and to subsequently come out duringsolidification of the metal after teeming to cause gas-pockets and likedefects, all as more particularly indicated in the Patent No. 1,925,916granted to William Bell Arness' on September 5, 1933 and entitledProcess of producing alloys.

In order to achieve temperatures sufficiently high to effectively meltthe refractory ingredients comprising the charge, an electric arcfurnace is preferably employed as a means of heating and furnacing theingredients. Conveniently, a Heroult furnace, or other furnace of thedirect arc type, employing carbon or graphite electrodes and lined withchromite brick to a height somewhat above -the slag line and havingside-walls and roof of silica brick is used in this practice.

Prior to charging the ingredients into the electric arc furnace, thefurnace is preheated in any suitable manner, as by arcing the furnace onelectrode butts or by means of a gas torch. After the furnace bottom andwalls have been adequately preheated, the preheating means are withdrawnand the raw materials, indicated above, comprising the initial charge ofingredients for a heat of high chromium high manganese iron or steel arecharged into the furnace.

In the production of a heat of high chromium high manganese iron orsteel to a desired specification of chromium, manganese and carboncontents (with or without one or more supplementary additions of nickel,copper, aluminum, silicon, molybdenum, tungsten, vanadium and the likein specified amounts), the relative amounts of chromium contributed bythe chromium-containing iron or steel scrap, high carbon ferrochrome andchrome ore, and the relative amounts of manganese contributed by themanganese-containing iron or steel scrap, high carbon ferromanganese andmanganese ore, all as used in proportions consistent with good furnaceoperating conditions, are largely determined by the availability ofthese various ingredients and the respective current market prices.Ordinarily the contained chromium is least expensive in the form ofchrome ore, is more expensive in the form of chromium-containing iron orsteel scrap and is most expensive as high carbon ferrochrome. Chromiumin all of these forms, however, is much less expensive than chromium asthe generally used low carbon ferrochrome. Similarly, manganese is leastexpensive in the form of manganese ore and progressively more expensiveas manganese-containing scrap iron or steel, high carbon ferromanganeseand the generally used low carbon ferromanganese.

To achieve clean, sound, high grade metal at a minimum of expense, amaximum of the less expensive chromium-containing andmanganesecontaining ingredients as is consistent with good furnaceoperation conditions (greatly limited by the permissible volume of slagwhich may be handled) is therefore employed. Now, since thechromium-bearing ingredients are considerably more expensive than themanganese-containing materials, and since the cost differential betweenchrome ore and high carbon ferrochrome is appreciably greater than thatbetween manganese ore and high carbon ferromanganese a maximum of theinexpensive chrome ore is preferably used in the practice of myinvention.

Where the practice indicates that further volumes of slag may beadequately handled, as in the production of the high chromium highmanganese irons and steels of the lower ranges of chromium and manganesecontents, much of the addition of manganese may be made in the form ofthe inexpensive manganese ore. Practice has shown, however, thatunsatisfactory furnacing conditions are encountered where the chromiumand manganese additions are made by chrome ore and manganese orerespectively, as for example, in the production of the high chromiumhigh manganese irons and steels of a medium range of analyses.

Highly satisfactory results are achieved in the production of highgrade, inexpensive metal by employing a maximum of chrome ore for thechromium addition and the readily available high carbon ferromanganeseas the source of manganese. In many instances, as in the production ofthe high chromium high manganese irons and steels of the upper analysesranges of chromium and manganese, much of the chromium is added in theform of high carbon ferrochrome.

Where desired the additions of chromium and manganese may be largelymade in the form of high carbon ferrochrome and high carbonferromanganese respectively, or as high carbon ferrochrome-manganese,substituting in whole or in part for additions of chrome ore andmanganese ore. Under present market conditions, however, the use ofgreat quantities of high carbon ferrochrome and high carbonferromanganese as sources .of chromium and manganese is found to'beappreciably more expensive than the use of substantial quantities of theores of chromium andmanganese for making these additions.

In the practice of my process for producing high chromium high manganeseirons and steels the amount of high chromium high manganese iron andsteel scrap employed as a source of chromium and manganese (ascontrasted with the high manganese steel scrap-10% manganese, 1% carbonand the balance ironwhich is well known and readily available) isgenerally determined by the availability of scrap metal in and aroundthe melt shop and various customer plants. As more particularlyindicated in the recently granted Patent No. 2,056,162 of William B.Amess, issued October 6, 1936, and entitled Production of rustless iron,the amount of scrap metal available in balanced manufacture in the formof ingot butts, crop ends and the like, is about 20% of the tappedmetal. Where this metal is processed into bar stock the available scrapis then about 25% to 30% of the tapped metal. Where the metal is furtherprocessed into sheet and strip at various customer plants for example,the scrap available as ingot butts, crop ends, scrap sheet, punchings,clippings and the like amounts to from 40% to 50% of'the metal tapped.This figure may even amount to some 60% or 70% where the sheet or stripis fabricated into various ultimate articles of manufacture, such asmachine or burner parts, kitchen ware, automobile trim, architecturalapplications and similar products.

While as an economical measure the amount of high chromium highmanganese iron or steel scrap employed in the production of a heat ofmetal is proportional to that rendered available about the melt shop,this amount may be greatly increased where large quantities of thisscrap are available at a favorable market price and similarly, theamount of scrap employed may be greatly lessened, or omitted entirely,where an acute shortage of scrap is encountered or where the marketprice of scrap becomes excessive.

The highly flexible nature of my. process of producing high chromiumhigh manganese irons and steels assures the production of high grademetal at a minimum of expense by using a maximum of inexpensive rawmaterials, the relative proportions of which are varied as desired tomeet fluctuating conditions of availability and market price.

As illustrative of the practice of my invention, in the production of aheat of high chromium highmanganese iron to a desired specification ofchromium 17.0% to 19%, manganese 8% to 10%, usual silicon, sulphur andphosphorus and the balance iron, 4,000 pounds of low carbon steel scrap,6,700 pounds of chromium manganese iron scrap (having an averageanalysis of chromium 17.5%, manganese 10.0%, carbon .12% and the balancesubstantially iron), 3,000 pounds of chrome ore (48% CrzOz), 800 poundsof high carbon ferrochrome (analyzing 4% to 6% carbon, 70% chromium andthe balance iron), 2,500 pounds of ferromanganese (analyzing 6% to 8%carbon, 80% manganese and the balance iron), and 4,000 pounds of rollscale, are charged onto the bottom of a chromite lined 6-ton three-phaseHeroult electric arc furnace rated 25 cycles, 120 to 180 volts, 2500kva. preheated as indicated above.

. Alternating current electrical energy is supplied the furnace and thecharge of ingredients begins to melt down forming individual pools offerrous metal containing carbon, chromium and manganese immediatelybeneath the furnace electrodes. Under the continuing action of theintense heat of the electric furnace arcs the melting charge ofingredients soon forms a single bathof ferrous metal containingconsiderable quantities of chromium and manganese and apthe slag andmetal and with a consequent 'minimization of the amount of carbondirectly con tributed to the metal bath. This is a feature ofconsiderable practical importance where the elimination of carbonrequires the use of additional materials and the expenditure of muchtime and effort.

The amounts of chromium and manganese present in the bath of .metal atthis stage of the process are largely dependent upon the amount of highchromium high manganese iron or steel scrap added to the charge (and theaverage chromium and manganese contents of this scrap) and the amount ofhigh carbon ferrochrome and high carbon ferromanganese melted down.Likewise, the quantities of chromium oxide and manganese oxide presentin the slag overlying the bath of metal are in a great measure dependentupon the amounts of chrome ore and manganese ore present in the initialcharge of ingredients.

The quantities of chromium and manganese appearing in. the metal bath asthe alloying elements, as compared with the amounts of chromium andmanganese appearing in the slag as oxides of chromium and manganese, arefurther dependent upon the oxidizing character of the slag overlying themetal bath and the tendency for this slag to oxidize these elements fromthe bath under the operating conditions encountered in practice. Theexcessive loss of chromium and manganese into the slag as oxides ofthese elements is effectively prevented, as appears more fullyhereinafter, by conducting the melting operation at a temperature ofsuper-heat and by initially proportioning relative amounts of chromiumand manganese going to form the metal bath and the overlying slag.

The strongly oxidizing character of the slag blanket overlying the bathof metal throughout the period of meltingdown of the charge ofingredients is effective in oxidizing the carbon supplied the bath ofmetal by the low carbon steel scrap, the chromium-containing ormanganesecontaining iron or steel scrap and the high carbon ferrochromeand the high carbon ferromanganese. The practical difficulties inoxidizing carbon fromthe metal are greatly lessened where -metal to pickup carbon from the electrodes is reduced to a minimum since manganesedoes not have the thirst for carbon that is characteristic of chromium.

The strongly oxidizing character of this slag furthermore acts as aneffective barrier between the bath of metal and the furnace carbon orgraphite electrodes to prevent the pickup of carbon from theseelectrodes in spite of the great avidity of a chromium-containingferrous metal bath for this element.

In order to minimize the oxidation of chromium and manganese from themetal bath incident to the removal and/or exclusion of carbon, themelting operation is preferably conducted at a high melt-downtemperature. The use of these high operating temperatures, which forconvenience I designate as temperatures of superheat, furthermoreassures a very active oxidation of carbon from the metal bath and therealization of an extremely low carbon .product in a minimum of time andwith the consumption of a minimum of power.

While no reliable method is known to me for precisely determining thetemperatures of metal and slag during the melt-down period, it isestimated that these temperatures are from about 3100 F. to 3250 R,which is some 150 to 300 F. higher than those ordinarily encountered inordinary electric steel making practices. The use of such extremely highoperating temperatures is permitted, as indicated above, by the highlyrefractory nature of the chromite brick furnace lining employed.

The excessive oxidation of chromium and manganese from the metal bath,which is ordinarily incidental to the oxidation of carbon, is furtherlessened by the inhibiting effect of the large quantities of chromiumand manganese present in the slag as oxides of chromium and manganese.The tendency toward the oxidation of these alloying elements from themolten metal is greatly lessened by the initially high balance betweenthe molten chromium and manganese oxides in the slag overlying the metaland the oxides of chromium and manganese dissolved in the metal. In thismanner certain further savings are realized in material and laborrequired to recover chromium and manganese from the slag, as moreparticularly described hereinafter, thereby achieving a highly efficientand economical process.

When the charge of ingredients is completely melted down and samplestaken from the bath for purposes of analysis indicate that the carboncontent is several points below the maximum value permissible themelt-down period is at an end. At this stage of the process, there areavailable in the slag great quantities of iron, chromium and manganesein the form of oxides of these metals, although much of the iron oxidein the slag has been lost during the melt-down oxidation period inremoving and/or excluding carbon from the melting metal and in theoxidation of chromium and manganese incidental to the oxidation ofcarbon, all as more particularly described above. The large quantitiesof metal which are found in the slag as oxides at this stage of theprocess, are recovered in a reducing period, where preferably anon-carbonaceous reducing agent, such as ferrosilicon, chemically inexcess of the oxides of iron, chromium and manganese contained in theslag, is charged onto the slag overlying the bath of metal. The preciseamount of reducing agent required to-effect a high recovery of themetals from the slag is ordinarily determined empirically.

The contamination of the metal bath with the silicon of the reducingagent during this stage of the process is efiectively prevented in spiteof the use of the excessive quantities of silicon, by conducting thereduction under strongly basic slag conditions. The desired basicconditions are preferably achieved by burnt lime in an amount of aboutthree to five times the total silicon content of the ferrosiliconemployed. Burnt lime, preferably predried to free the limeof-substantially all free and combined moisture normally present, isconveniently charged onto the slag along with the silicon-containingreducing agent.

For the illustrative charge of ingredients set forth above 2,500 poundsof crushed ferrosilicion of the 75% grade and 8,000 pounds of predriedburnt lime are charged onto the slag overlying the bath of metal.

Prior to charging the silicon reducing agent and lime onto the slag,these ingredients are conveniently mixed on the floor of the melt shop.This mixture is then charged onto the slag overlying the bath of metalfrom time to time as furnace conditions permit. By charging a largeproportion of burnt lime along with the reducing agent in this mannerthe maintenance of strongly 'basic slag conditions during the reducingstage of the process is assured.

By carrying out the-reduction of the oxides contained in the slag understrongly basic conditions silicon contamination of the metal isprecluded. The acid silicates resulting from the reduction of thereducible oxides of the slag by the silicon reducing agent employedreact with the basic lime added to the slag and form a series of calciumsilicates, all as more particularly described in the Patent No.1,932,252 of William B. Arness, granted October 24, 1933 and entitledProcess of producing alloys. These calcium silicates are among the moststable components of the slag.

The large quantities of burnt lime charged onto the slag overlying thebath ofmetal during the reducing period, as more particularly describedabove, serve not only to render the slag strongly basic and preventsilicon contamination of the metal but also serve to give body to theslag (which is highly fluid and watery because of the large percentageof manganese oxide present in the slag) which in a manner not fullyunderstood by me is effective in achieving a highly eflicient reductionof the reducible oxide content of the slag.

The continued heating of the metal and slag during the prolongedreducing period affords an opportunity to melt down further quantitiesof chrome ore and manganese ore. These materials are preferably chargedalong with 'the silicon reducing agent and burnt lime in correspondingsuccessive batches. The addition of chrome ore and/or manganese ore atthis stage of the process permits the use of a maximum quantity of thesecheap sources of chromium and manganese (a feature particularlyimportant in the produc-- tion of high chromium high manganese irons andsteels of the higher chromium and manganese analyses) while maintaininga manageable volume of slag within the furnace throughout both the meltdown oxidation period and the subsequent reduction period with a minimumsubmersion of the furnace electrodes in the furnace metal therebylimiting objectionable carbon pickup from the furnace electrodesthroughout the complete process. Illustratively, 2,500 pounds of chromeore and 200 pounds of pyrolusite (MnOz) are charged along with theferrosilicon and lime.

After all of the reducing agent, burnt lime and chromium and manganeseores have been added and have fused and completed their reactions withthe ingredients present in the slag and metal and a substantiallycomplete recovery of the oxides of chromium and manganese contained inthe slag is achieved, as evidenced by a (ill the final silicon contentof the metal.

change in color of successive samples taken from the furnace from ablack to a light green or gray, the reduction stage of the process is atan end. The slag overlying the bath of metal from which iron, chromiumand manganese are completely recovered is then completely drawn off themetal.

A basic finishing slag of burnt lime and fine ferrosilicon is scatteredover the exposed surface of the metal bath. (About 500 pounds of burntlime and about pounds of the 75% grade ferrosilicon are employed for theexample given.) The heating of the bath is continued at the reducedpower input necessary to maintain the metal at a desired temperatureuntil the refining of the metal is completed. The necessary duration ofthe refining period is greatly decreased in the production of highchromium high manganese steels because of the presence of a largepercentage of manganese in the metal which is effective in refining andcleansing the metal of distributed oxides. During this period lumpferrosilicon is added as desired to adjust In the example given, about50 pounds of 75% ferrosilicon is used to make the final adjustment ofthe silicon content of the metal.

After the desired refining of the metal is effected the application ofpower to the furnace is discontinued, the furnace electrodes are raisedand the heat of metal is tapped into a ladle for teeming. There isproduced about 18,200 pounds of high chromium high manganese iron ingotsanalyzing approximately, .07 carbon, 17.2% chromium, 9.8% manganese,.50% silicon with the usual percentages of sulphur and phosphorus andthe balance substantially iron. The metal is clean, sound andcomparatively free of objectionable oxide inclusions.

Where desired supplementary additions of nickel, copper, aluminum,silicon, molybdenum, tungsten, vanadium, zirconium and the like may bemade in accordance with standard practice either in the furnace or inthe ladle.

The production of high chromium high manganese irons and steels with aminimum repair and/or replacement of furnace linings and a minimumfurnace shut-down and loss of operating time, is enjoyed by virtue ofthe chromite lining employed. This linin'g, as compared to heretoforeknown and/or used linings, is particularly resistant to destructiveattack, at the high temperatures employed, by.the oxidizing melt-downslag followed by the reducing slag used in the second stage of theprocess, all as more particularly pointed out in my Patent No.1,925,182,

granted September 5, 1933 and entitled Process the slag from which thereducible oxides are effectively recovered, supplying iron and chromiumto the bath of metal, thus, in a measure, compensating for the cost ofthe erosion of the lining.

Thus, it will be seen that there has been pro- .vided in this inventionan art of producing high chromium high manganese irons and steels andespecially the produc'tionof high chromium high manganese irons (metalin which the carbon ploying a maximum of available and inexpensive rawmaterials consistent with the realization of good furnace operatingconditions and the production of clean metal. Because of the presence ofa high percentage of manganese in the metal, and the tendency formanganese to reduce chromium oxides, larger quantities of theinexpensive source of chromium, chrome ore, are effectively used withoutrisking the production of dirty metal, objectionably contaminated withoxides.

It will be further seen that the process is particularly favorable toobtaining a desired economic balance between the raw materials employedas sources of the alloy metals, chromium and manganese, by relativelyadjusting the proportions of ingredients (to such an extent as isconsistent with the maintenance of good furnace operating conditions)chromium, manganese iron or steel scrap, chrome ore and high carbonferromanganese, in accordance with variations in the availability ofthese materials and the fluctuations in their market prices.

While as illustrative of the practice of my invention substantialquantities of chrome ore and manganese ore are added both along with theinitial charge of ingredients melted down and, with the reducing agentadded after meltdown is complete, in order to take advantage of thecomparatively long melt-down and reduction periods to effect a thoroughheating of these refractory ingredients, it will be understood thatchrome ore and/or manganese ore may be added while the melt-down periodis in progress, especially toward the end of this period when samples ofmetal have been taken and the heat of metal is being held in the furnaceawaiting a report 'of the carbon analysis, in order to realize thebenefits of the available furnace heat during this period. Likewise, itwill be understood that where furnacing conditions permit substantiallyall of the ore may be added during the melt-down period, thus in ameasure simplifying the procedure.

As many possible embodiments may be made of my invention and as manychanges may be made in the embodiments hereinbefore set forth, it willbe understood that all matter described herein is to be interpreted asillustrative and not in a limiting sense.

I claim:

1. In the production of-high manganese rustless irons and steels in anelectric arc furnace, the art which includes, melting down in saidfurnace iron scrap, high carbon ferromanganese and chrome ore therebyforming a bath of ferrous metal containing manganese and chromiumcovered by a slag containing the oxides of iron and chromium, and aftermelt-down is complete reducing the oxides contained in said slag therebyeffecting an enrichment of the bath in chromium.

2. In the production of high manganese rustless irons and steels in anelectric arc furnace,

- the art which includes, melting down in said furnace iron scrap, highcarbon ferromanganese and chrome ore thereby forming a bath of ferrousmetal containing manganese covered by a. slag containing the oxides ofiron and chromium, bringing said bath of metal and the overlying blanketof slag up to a temperature of superheat thereby oxidizing and/orexcluding carbon from said bath, and after melt-down is complete and thebath has reached a desired low carbon content reducing the oxidescontained in said overlying blanket of slag thereby effecting anenrichment of the bath in manganese and chromium.

3. In the production of high manganese rust- 10 less irons and steels inan electric arc furnace,

the art which includes, melting down in said

